Logging boreholes has been done for many years to enhance recovery of oil and gas deposits. In the logging of boreholes, one method of making measurements underground includes attaching one or more tools to a wireline connected to a surface system. The tools are then lowered into a borehole by the wireline and drawn back to the surface (“logged”) through the borehole while taking measurements. The wireline is usually an electrical conducting cable with limited data transmission capability.
Demands for higher data transmission rates for wireline logging tools is growing rapidly because of the higher resolution, faster logging speed, and additional tools available for a single wireline string. Although current electronic telemetry systems have evolved, increasing the data transmission rates from about 500 kbps (kilobit per second) to 2 Mbps (Mega bits per second) over the last decade, data transmission rates for electronic telemetry systems are lagging behind the capabilities of the higher resolution logging tools. In fact, for some combinations of acoustic/imagining tools used with traditional logging tools, the desired data transmission rate is more than 4 Mbps.
One technology that has been investigated for increased data transmission rates is optical communication. Optical transmission rates can be significantly higher than electronic transmission rates. However, the application of optical fibers to the rigors of an oilfield environment have proved to be a significant hurdle. Compounding the problem of using optical fiber in an oilfield environment is the typical need for multiple fibers for most communications applications. In prior oilfield optical applications, one or more optical fibers is used for downlink commands, and one or more additional fibers is used for uplink data. The use of multiple optical fibers increases chance of a failure of at least one of the fibers or a failure at connections to the fibers, especially in an oilfield environment. Therefore, there is a need for an single-fiber optical telemetry system.